The present invention broadly relates to paving machines for evenly applying and distributing cementitious flowable materials. More particularly, the present machine relates to road surfacing equipment adapted to resurface or overlay existing roadways with polymer concrete materials. Prior art pertinent to the present invention is classified in U.S. Classes 404 and 94.
The placement of concrete for roadways and highways has evolved over the years. Initially concrete roadways were placed much like any other slab, with the use of static forms and hand manipulated finishing tools. Eventually, machines were developed to assist in the distribution of the concrete. Such devices usually employ a set of sliding, edge forms that assist in forming the roadway. These slip form pavers also employ integral troweling or screeding devices to smooth the surface of the concrete. Typically such conventional pavers use concrete of relatively low slump. As will be appreciated by those skilled in the art, low slump concrete is necessary in highway construction. First, the placed concrete can maintain its shape after the forms associated with the slip form paver move out of contact with the plastic concrete. The cured strength of Portland cement concrete used in highway construction is approximately 4,000 PSI. Conversely, in polymer concrete, the strength is approximately 8000-10,000 PSI, and polymer concrete exhibits a high slump.
A typical slip form paver is disclosed by G. W. Maxon, Jr. in U.S. Pat. No. 3,043,201 issued Jul. 10, 1962. As will be noted upon inspection of this patent, the art of the day was concerned with handling low slump concrete. The design was primarily aimed at avoiding segregation of the aggregate, and handling the relatively thick mixture.
Modern technology plays a role in many present day paving operations. U.S. Pat. Nos. 4,854,769 and 4,861,189 both issued to Mitsuo Fukukawa teach a rather complicated system of paving inclined and curved surfaces. The devices disclosed by Fukukawa employ an anchoring vehicle and a paving vehicle. The paving vehicle is connected by cables to the anchor vehicle. The paving vehicle has a laser transmitter and the anchor vehicle has a laser receiver. The relative arrangement of the two vehicles is controlled by microcomputer that operates a boom on the anchor vehicle to control the height and length of the cable connecting the two vehicles. Further, a screed on the paving vehicle is controlled by a microcomputer to shape the surface of the roadway.
Kasler U.S. Pat. No. 4,988,233 issued Jan. 29, 1991, discloses another modern paving machine. The disclosed machine is primarily intended for paving in zero or minimum clearance applications. It employs a conventional tracked vehicle coupled to a pan assembly which distributes and surfaces the concrete. As will be apparent upon inspection of this patent by one skilled in the art, this machine is intended to distribute relatively low slump concrete. It employs the surface of the subgrade or existing roadway to help move the concrete using augers to distribute the concrete to be worked by the finishing elements of the machine. In other words, concrete is dumped in front of the machine. As it pulls over the concrete it spreads and finishes it.
Three U.S. Patents assigned to the same entity as the present invention are U.S. Pat. Nos. 4,249,327; 4,466,757 and 4,798,494 share a common inventor J. Dewayne Allen. U.S. Pat. No. 4,249,327 issued Feb. 10, 1981 discloses a vibratory screed incorporating a fine grader. A vibratory screed employing a spreading device disposed perpendicular to the screed is disclosed in U.S. Pat. No. 4,466,757. U.S. Pat. No. 4,798,494 discloses a floating vibrational screed comprised of a strike off portion and a pan portion.
As in the present invention machine elevation is controlled by a relatively conventional string line system. Such string lines are strung at an elevation relative to the desired elevation of the new roadway. The paving machine has sensors or "wands" that contact the string on either side of the vehicle to provide sensor data to electromechanical components of the machine controlling the relative height of the finishing components of the machine.
The use of polymers in place of cement in concrete mixtures to provide a high strength abrasion resistant surface is well known. The proper placement and curing of polymer pavement is an evolving "hi-tech" solution to the deterioration of our nation's roadways. Polymer concretes are comprised of aggregates, sand, various polyester or polymer resins known to those skilled in the art, and one or more organic hydrocarbons, such as methyl-ethylketone peroxide (MEK-P), that functions as a catalyst. While relatively expensive, polymer concrete exhibits desirable strength-to-volume relationships that make it ideal for resurfacing bridges and bridge approaches. Much experimental use of such polymer concrete in the highway industry has taken place over the last decade. Polymer concrete technology has evolved to the point that it is now being routinely specified for resurfacing jobs where the overall weight of the roadway bed is of prime consideration. Examples include highway structures such as bridges, bridge approaches, causeways and elevated roadways.
Many roadways and interstate highway systems that have weak and deteriorating road surfaces are essentially structurally sound. In many cases, it is only the first few inches of pavement that must be replaced and resurfaced. With conventional concrete or asphalt, it is difficult to bond the outer replacement surface to the underlying bed. If surface repairs are made with conventional materials, pot holes and cracks quickly appear. The latter problem is avoided with polymer paving materials. Proper use of polymer pavement where the underlying structure and bed of the roadway are sound obviates the necessity to replace the entire roadway and completely rebuild the road structure. Polymer concrete is normally applied in a relatively thin overlay ranging in thickness from one quarter inch to one and a half inch. A simple resurfacing with polymer concrete will provide ten to fifteen more years of use for the bridge or elevated roadway.
Moreover, polymer pavement has superior wear characteristics, it is waterproof and has a higher cured strength than Portland cement concrete. Additionally, polymer concrete has a relatively high slump that is well suited to applications such as bridge approaches and exits, where the roadway bed is banked, curved, or inclined. Polymer concrete can be applied to a rough road surface to fill relatively rough contours without entraining the air pockets that would result if conventional concrete were employed. Slump is often as much as six inches. While many problems related to the handling of low slump concrete have been addressed by the prior art (i.e., slip form pavers), new problems arise when dealing with such a high slump material.
First, high slump material cannot be moved about as easily as the low slump concrete addressed in prior art solutions such as the Kasler patent. As mentioned above, Kasler employs a concrete hopper and augur which have no bottom surfaces. In other words, Kasler employs the ground as the bottom of its hopper and auger housings. High slump polymer concrete cannot be piled in front of the auger as can low slump concrete.
Therefore, it is necessary to provide a hopper on the vehicle and a trough or passageway for the polymer concrete to be transported through. Furthermore, to evenly distribute the concrete transversely it is necessary again to use augers to move it. Additionally, the problem with segregation is even greater with high slump concrete than with low slump concrete. Due to the thinness of the mixture it tends to settle out relatively fast. Hence, it is necessary to continually agitate the concrete from the time it is placed in the hopper until it is delivered to the road surface.
As mentioned above, polymer concrete is usually used for resurfacing purposes. Therefore, it is disposed in a relatively thin layer. The surface of an existing concrete roadway is "shot blasted" or stripped away down to expose a bonding surface, sometimes to the upper surface of the rebar itself. Damaged rebar is repaired. A polymer bonding agent is applied to the exposed surface and allowed to cure prior to the pour. As a result, a relatively rough surface of exposed aggregate is left remaining for the polymer concrete to cover.
As will be appreciated by those skilled in the art, the placement of a thin overlay is in many ways more difficult than the placement of a slab of four to eight inches of thickness. Simply stated, the acceptable margin of error when pouring a one inch slab is much smaller than the margin of error when pouring an eight inch slab. Therefore, precise grade control is necessary.
Additionally, modern paving operations must take into account the need for continued use of an existing roadway. Often paving operations must be accomplished in a relatively short time frame at night, between traffic "rush hours." In fact, some states, such as California, require that its highway contractors perform work at night. Polymer concrete helps to accomplish this goal. Within four hours of placement it is ready for traffic. Therefore, resurfacing work can be finished during the night hours, and the repaired roadway can then endure rush hour traffic the very next morning.
Often it is necessary to repave only a single lane of a roadway while immediately adjacent lanes are still in use. Therefore, it is necessary that modern paving equipment be designed for compact, single lane use. The components of the machine need to be relatively narrow in width and adjustable to accommodate varying lane widths and shoulder configurations. Furthermore, the use of narrow components for such a machine facilitates paving adjacent to structures. For example, if the motive means of the paver is narrower than the lateral distribution components, it's related finishing components can place and finish a slab abutting a standing guard rail or retaining wall.
Polymer pavement, due to its nature and the applications for which it is employed, must be compacted to a relative density of ninety-eight to one hundred percent. While its high slump facilitates such compaction it is still necessary that it be properly handled. One means for reaching such compaction is to "squeeze" the mixture upon placement. Additionally, vibration helps to free any trapped air pockets and of course provides a uniform finish. On roadways such a smooth, uniform finish must necessarily be etched to provide traction for vehicles.
It is thus desirous to provide a polymer paver machine that is capable of distributing polymer concrete in varying widths, while maintaining the blend of its constituents. Furthermore, it is desirous to provide a machine that can work fairly quickly to take full advantage of the quick setting nature of the polymer concrete. A rapid rate of placement is required for polymer concrete in order to place, consolidate and finish the surface prior to chemical transformation of the polymers.
It is further desirous that the machine be capable of fine grade control to provide a uniform thickness with a relatively high slump polymer concrete. Finally, it is important to provide a machine that is capable of placing flowable paving materials in a layer that is not necessarily rectangular. In other words, it may be necessary to lay material in a layer that has a trapezoidal cross-section. Ease of use, precise deposition rate, controllable surface finish and rapid rate placement are important aspects of a practical polymer paver. Variable width paving capability, ease of clean up, and minimum maintenance are other desirable features embodied by the herein disclosed equipment.